1. Field of the Invention
The present invention relates to a radar beacon apparatus used for position location during emergency rescue operations.
2. Description of the Prior Art
In the past, radar wave reflectors such as a corner reflector have been considered for the radar beacon application.
However, large background noises caused by reflections off ground and sea surfaces necessitated a larger and larger radar wave reflector and related passive radar apparatus to identify the ordinary echo of a ship or and echo in distress.
In order to overcome this disadvantage, active beacon systems have been proposed. A typical active beacon system is seen in FIG. 1 to consist of a small size high frequency oscillator (2), such as a high frequency diode oscillator, connected to an antenna (1), a FM modulation signal source (3) for varying the oscillating frequency of the high frequency oscillator (2) and a power source (4) for operating these devices. The high frequency signal which is generated by the high frequency oscillator (2) and the FM modulation signal source (3), is included in the carrier frequency fo the pulse modulation type search radar (6) provided on a search and rescue vessel (5). The repeat cycle of the FM modulation signal has a desired value relative to the repeat frequency and pulse width of the pulse modulation wave of the radar wave, and the bright lines (a) of FIG. 3 indicate the direction of the target on a radar display of the search radar (6).
In the beacon system of FIG. 1, it is therefore seen that the direction for search can be determined by the bright lines (a) of FIG. 3, however it is difficult to isolate the position of the target on the bright lines. Furthermore, since this is a continuous oscillating type apparatus, even though a small size high frequency oscillator can be used, the load to the power source (4) is remarkably high and a large size power source is disadvantageously required for operation over a long time period.